Total synthesis of (-)-steganone utilizing a samarium(II) iodide promoted 8-endo ketyl-olefin cyclization

A six-step synthesis of (+/-)-steganone from commercially available 3,4,5-t rimethoxybenzyl alcohol features a samarium(II) iodide promoted 8-endo kety l-olefin coupling to install, in a single transformation, the 8,5 ring syst em common to the Lignan lactones. The racemic synthesis provided the basis for the construction of (-)-steganone, which exploited a chromium tricarbon yl moiety both to establish and protect the desired absolute stereochemistr y through key transformations, including a SmI2-promoted 8-endo radical cyc lization and two palladium-catalyzed couplings.